Typically, small robots having round wheels can run through a narrow clearance and may be efficient in searching a survivor in a place such as a collapsed building or finding an enemy base during a military operation.
However, a small robot that uses round wheels cannot climb an obstacle taller than the radius of the round wheels.
As an alternative, legged-wheel robots have been proposed for their better climbing performance. However, such legged-wheel robots have poor driving performance on flat surfaces since their center of mass is vertically changed.
Thus, there have been proposed robots having transformable wheels which can drive with round wheels on flat surfaces and can climb an obstacle with legged wheels.
As one background art of the present invention, there is disclosed an exploration-purpose robot that includes a plurality of leg units for supporting a body unit and enabling the robot to walk, each of the leg units including a calf portion, a thigh portion and a plurality of drive joints. The exploration-purpose robot further includes a control unit for operating and controlling the joints of the leg units. The calf portion of each of the leg units is provided with a foot for walking at one longitudinal end thereof. A ball caster for wheel driving is provided at one side of the calf portion. A rotating joint means for selectively operating the foot and the ball caster is provided at the center of the calf portion.
However, the exploration-purpose robot is merely designed to enhance the moving efficiency by freely selecting a foot's rolling operation and a ball caster's sliding operation depending on the walking environment of the robot. Since the wheel-driving-purpose ball caster used as a moving means exists in the calf portion, the ball caster serving as a wheel cannot passively transforms in conformity with the shape of a terrain. Moreover, the exploration-purpose robot is very complex in configuration. It is therefore difficult to use the exploration-purpose robot in a small robot application.
As another background art of the present invention, there is disclosed a transformable wheel that can drive on flat surfaces and can climb stairs. The transformable wheel includes: a rim; a plurality of spokes installed inside the rim and fitted at one ends to the rim so that the free ends thereof can protrude outward of the rim; and a gear box. The gear box includes: a rim gear portion for delivering the power of a motor to the rim; a spoke gear portion for delivering the power of the motor to the spokes; and a movable gear portion disposed between the motor, the rim gear portion and the spoke gear portion so as to selectively mesh with the rim gear portion and the spoke gear portion.
In the transformable wheel cited above, the complex gear box including the motor-operated spoke gear portion for expanding the spokes outward of the rim is mounted to the wheel. Therefore, additional power needs to be used in order to drive the gear box. It is also impossible to automatically expand the spokes to adapt themselves to the terrain features.
That is to say, the transformable wheel cited above has a complex structure because of the use of a large number of parts, such as a displacing actuator and a rotating actuator, for driving the rim and expanding the spokes. A battery having a large capacity is needed to operate the displacing actuator and the rotating actuator. Therefore, the transformable wheel cited above is not suitable for use in small robots.